I would love a way to do that inside. I think it is practically impossible if you want to keep a halfway neat shop. I have always case hardened outside. Even small packs make a big mess. When I use my new crucible that is big enough for an entire lock, I am going to plug-in my heat treat oven outside in my forge area. I have my post vise mounted on a small bench that will accommodate my oven and has an electric outlet next to it. When I get ready to dump that thing (in my regular five gallon quench tub next to the anvil), I will be wearing overalls, long sleeves, a leather apron, leather gloves and a face shield. Hopefully, I won't catch my overalls on fire. That is because all that red hot charcoal will be blown back in my face and all over. If the forge wasn't already a mess, It would be black after that, and so will I. I will have to strip and put my clothes in the washer just inside the back door.